Various methods of improving the high temperature resistance of vitreous materials are well known. Particularly important in this field are those methods in which a refractory metal oxide is deposited on the surface of glass fibers.
U.S. Pat. No. 2,901,379 is directed to the use of metal oxides having a melting point of at least 1000.degree. C. and defines as suitable oxides Fe.sub.2 O.sub.3, MgO, Cr.sub.2 O.sub.3 and the like.
U.S. Pat. No. 3,232,782 suggests coatings consisting essentially of at least one compound selected from the group consisting of the oxides and silicates of chromium, aluminum, zirconium, titanium, and metals of Group II of the Periodic Table having an atomic number from 4 to 12.
U.S. Pat. No. 3,449,137 suggests the fusing into the glass of specific amounts of chromic oxide with a very limited range of relative proportions of alumina and silica.
U.S. Pat. No. 4,169,182 states that effective substances for absorbing radiant heat energy are metals such as Cu, Co, Fe, Cr, Mn and Ni and these materials can be either mixed in the glass raw materials and thereafter forming the mixture into fibers, or by forming a coating film of such materials or their oxides on the glass fibers.
The deposition of such metals on glass fibers, while improving the temperature resistance of the fibers, produced fibers having limited flexural properties.